Separation device comprising a tubular electrocoalescer

ABSTRACT

The present invention relates to a device for separating an effluent comprising phases of different density and conductivity, the device comprising a pair of electrodes ( 12, 13 ), means ( 10 ) for introducing the effluent between said electrodes, means intended for separation ( 3 ) and discharge ( 4 ) of said separated phases. The separation means comprise at least one centrifugation element including a helical channel ( 19 ) in which the effluent is centrifuged after passing between the electrodes. An opening extends over the entire periphery of said centrifuged effluent so as to discharge part of the centrifuged effluent. The discharge means further comprise sealing means for limiting discharge of the less dense phase through said opening.

FIELD OF THE INVENTION

[0001] The present invention relates to the field of emulsified effluentprocessing, notably petroleum effluents from production wells. Theemulsions concerned are those whose disperse phase is electricallyconducting, unlike the continuous phase, for example water dispersed inan organic phase such as oil.

[0002] It is important to separate the water from the effluent producedso as to improve the quality, therefore the market value, of theeffluent and to limit the size of the processing and transportequipments. After passage of the emulsified effluent throughconventional water/oil separators, the effluent still contains about 1to 5% emulsified water in the oil. The goal of the present invention isto decrease these residual amounts of water and salts in order to meetthe technical requirements of the downstream processes.

BACKGROUND OF THE INVENTION

[0003] Document U.S. Pat. No. 5,647,981 describes a device whichcombines the principle of an electrocoalescer with centrifugation.

[0004] Water-in-oil emulsions can be “broken” by coalescence of thewater drops through the action of an electric field. However, in orderto increase the efficiency of these electrostatic separators, one triesto increase the electric potential between the electrodes, with a realrisk of appearance of breakdown phenomena between electrodes. On theother hand, considering the residence time required between theelectrodes, the effluent flow rate that can be treated is low, unless aninstallation of disproportionate size is used.

[0005] Document FR-2,824,489 discloses a combination between anelectrocoalescer of determined shape and centrifugation and separationmeans specific to said coalescer.

[0006] The present invention aims to improve the separation meansdescribed in document FR-2,824,489.

SUMMARY OF THE INVENTION

[0007] The present invention thus relates to a device for separating aneffluent comprising phases of different density and conductivity. Thedevice comprises a pair of electrodes, means for introducing theeffluent between said electrodes, a helical channel in which saideffluent is centrifuged, after passage between said electrodes, so thatthe phases are separated, and means intended for discharge of theseparated phases. The discharge means comprise an opening extending overthe periphery of said centrifuged effluent to discharge part of thecentrifuged effluent. The device is characterized in that the dischargemeans further comprise sealing means for limiting discharge of the lessdense phase through said opening.

[0008] The sealing means can comprise a mask closing said opening andleaving an orifice so that the denser phase distributed in the lowerpart of said channel is discharged through said orifice and the lessdense phase distributed in the upper part of said channel is kept insidethe discharge means by said mask.

[0009] The sealing means can comprise a surface converging towards theinside of the discharge means, so that part of the effluent dischargedthrough said opening is collected by said surface and fed into thedischarge means. This surface can be truncated-cone-shaped.

[0010] The orifice can extend over an angular portion ranging between20° and 180°.

[0011] The helical channel can consist of at least one helical wallarranged in an annular space. The end of the helical wall coincides withan edge of the orifice. The orifice can also extend on either side ofthe end of said helical wall.

[0012] The helical wall is in contact with the internal tube but it canprovide a clearance with the wall of the external tube.

[0013] The helical channel can consist of a helical tube.

[0014] The electrodes can have the shape of cylinders arranged along thesame axis.

[0015] The section of flow of said helical channel can be so determinedthat the velocity of the effluent increases in relation to the velocityof the effluent in the vicinity of said electrodes.

[0016] According to the invention, the less dense phase can bedischarged through an axial line.

[0017] According to the invention, the discharge means can comprise acyclone and an axial orifice for discharge of at least part of thecentrifuged phase.

BRIEF DESCRIPTION OF THE FIGURES

[0018] Other features and advantages of the present invention will beclear from reading the description hereafter of a non limitativeexample, with reference to the accompanying drawings wherein:

[0019]FIG. 1 diagrammatically shows the principle of the invention,

[0020]FIG. 2 diagrammatically shows the outlet of the separatoraccording to the invention,

[0021]FIG. 3 is a developed view of a part of the invention,

[0022]FIG. 4 shows in detail an element of the separator outlet,

[0023]FIG. 5 illustrates a variant of the centrifuge,

[0024]FIG. 6 shows the distribution of the oil and water phases at theseparator outlet.

DETAILED DESCRIPTION

[0025] The general layout of an example of embodiment of a deviceaccording to the invention meets the following requirements:

[0026] the fluid is preferably fed under pressure between twocylindrical and concentric walls, the tangential inlet is not essentialbut preferably maintained,

[0027] the electrocoalescer has a determined geometry allowing to obtaina sufficient residence time for the effluent. For example, its lengthcan be about 1 m and the annular space is such that the residence timeof the fluid is 10 seconds at a flow rate of 500 l/h. The distancebetween the cylinders is therefore 7.86 mm (radius difference between a2-inch tube (50.8 mm) and a 1-inch tube (25.4 mm)),

[0028] a centrifuge is arranged after the electrocoalescer, whose motiveelement is one or more helical surfaces arranged between two concentriccylinders over, for example, a length of 500 mm. For information, thedistance between the cylinders has been reduced to 6.35 mm (radiusdifference between a 1.5-inch tube and a 1-inch tube) in order toincrease the velocity of the fluid as it flows through the centrifuge,

[0029] the centrifuge opens onto a separator proper. This part isessential and of delicate design in order to prevent the intenseturbulence developed at the centrifuge outlet from dispersing the waterdroplets again.

[0030] In FIG. 1, which shows the whole of device 1 according to theinvention, reference numbers 2, 3 and 4 respectively refer to thecoalescer, centrifuge and separator parts. Arrow 5 shows the inflow ofthe effluent containing the emulsion into the device, arrow 6 shows theoutflow of the dehydrated effluent sent to transport and refininginstallations 8, arrows 7 show the various outflows of the essentiallyaqueous phase sent to discharge processing installations 9.

[0031] The means for feeding the emulsified effluent into the coalescerare such that the fluid is fed tangentially into annular space 11delimited by the outside of electrode 12 and the inside of shell 13. Thedimensions of the electrocoalescer, diametral and longitudinal, are sodetermined that, considering the rate of injection of the effluentthrough means 10, the residence time in the air gap of the electrodes issuch that the coalescence of the water drops is optimum. Electrodes 12and 13 are electrically connected to an electric field generator 14.Electrodes 12 and 13 are preferably cylindrical in shape. At the end ofthe coalescer, electric insulating means 15 separate the electrodes fromthe inlet means of centrifuge 3.

[0032] Centrifuge 3 consists of an external cylindrical tube 16,preferably vertical, an internal tube 17 in continuation with centralelectrode 12 of the coalescer, and a helical wall 18 in contact with theinside of tube 16 and the outside of tube 17 so as to form a continuoushelical channel 19 around the longitudinal axis of the device. The shapeof this channel 19 is such that the effluent at the coalescer outlet isled to be centrifuged over the total length of centrifuge 3. This lengthis furthermore determined to optimize the centrifuging effect. Conicalconnection means 20 can be used between the coalescer and the centrifugein order to reduce the main section of flow of the effluent so as toincrease the velocity of flow of the fluid in the centrifuge. The higherthe velocity, the better the centrifugation and therefore the phaseseparation.

[0033] In an equivalent way, the centrifuge can be obtained from a lineof suitable section with a helical shape for centrifugation of thefluid. At least one tube can for example be helically wound around atube.

[0034] Without departing from the scope of the invention, centrifuge 3can comprise several helical channels.

[0035]FIG. 5 shows a variant of the centrifuge wherein helical wall 18is not in contact with the inner wall of external tube 16. Clearance dallows formation of a layer of the centrifuged phase which can freelyflow also in the longitudinal direction, i.e. downwards when the deviceis arranged vertically, which is generally preferable.

[0036] A separation element 4 is fastened to the end of the centrifuge.Its purpose is to collect the water drops which are in contact with theouter wall by centrifugation. A conical part 20 forming a continuationof the centrifuge produces a cyclone type separation, the centrifugedphase being discharged through orifice 21, the lighter phase (organicphase) being discharged in the direction of the axis of the cone throughthe inner space of tube 17 extended by the inner line of electrode 12.Separation element 4 furthermore comprises a lateral opening surface 22allowing to separate the major part of the aqueous phase in contact withthe inner wall of tube 16.

[0037]FIG. 2 shows more in detail the separation means. The samereference numbers as in FIG. 1 are used in FIG. 2. Channel 19 isdelimited by two helical walls 18 a and 18 b separated by a distance hcorresponding to the height of channel 19. At the end of centrifuge 3,channel 19 opens into an annular volume 30 defined between the innersurface of tube 16 and the outer surface of tube 17. Volume 30communicates with collection volume 31 through opening 22 provided intube 16. The collection volume is delimited by the outside of tube 16and by divergent tube 35. It can be noted that end 23 of tube 17 isextended after opening 22. Opening 22 is preferably a complete ringextending over the periphery of tube 16 so that the major part of thecentrifuged aqueous liquid is discharged through this opening. Opening22 can be made by cutting out a portion of tube 16 between two planes.Thus, tube 16 is separated into two distinct sections: a sectionextending upstream from opening 22 and a section extending downstreamfrom opening 22.

[0038] Under the effect of centrifugation, the water, denser than oil,tends to spread and to circulate in the lower part of channel 19 whereasthe oil tends to spread and to circulate in the upper part of channel19. FIG. 3 shows channel 19 developed in a plane. The lower part ofchannel 19 rests on helical surface 18 a. The upper part of channel 19is delimited by helical surface 18 b separated by height h from surface18 a. The phases of the effluent at end 29 of channel 19 are separated.The water represented by the dotted volume circulates in the lower partof channel 19 over height h1. The oil represented by the hatched volumecirculates in the upper part of channel 19 over height h2.

[0039]FIG. 2 shows two means 32 and 33 intended to allow passage,through opening 22, mainly of aqueous liquid only and to keep the oil involume 30.

[0040] First means 32 consists of a surface extending in volume 31, forexample a truncated cone converging towards the inside of tube 16.Truncated cone 32 allows to collect part of the effluent that has passedthrough opening 22 and to feed it back into tube 16. Under the effect ofcentrifugation in channel 19, the oil phase that has flowed throughopening 22 in the direction shown by arrow F1 is collected by truncatedcone 32, then it is fed back into the inner volume of tube 16. Theaqueous phase, denser than the oil phase, circulates mainly in thedirection shown by arrow F2. The aqueous phase is not affected bytruncated cone 32 and it is discharged from volume 31 through an outlet7.

[0041] Second means 33, shown in dotted line in FIG. 2 and in detail inFIG. 4, consists of a mask which closes part of opening 22. Mask 33 canbe a tube portion inserted inside or outside tube 16. Mask 33 leaves anorifice 34. The position and the geometry of orifice 34 are so selectedthat the water circulating in the lower part of channel 19 is dischargedthrough orifice 34 and the oil circulating in the upper part of channel19 is kept in annular volume 30 by mask 33. For example, orifice 34extends over an angular portion θ ranging between 20° and 180° and overa height H ranging between 10% and 100% of the height h of channel 19.Orifice 34 can be positioned in relation to the end of helical surface18 marking the end of channel 19. For example, angular portion θ oforifice 34 is distributed on either side of the end of helical surface18. Or the end of helical surface 18 coincides with an edge of orifice34, orifice 34 extending over an angular portion θ from this edge in thedirection of rotation of the helix of channel 19.

[0042]FIG. 3 also shows mask 33 developed in a plane. Orifice 34 is sopositioned in relation to channel 19 that channel 19 mainly leads theaqueous phase to orifice 34.

[0043] One of the first and second means 32 and 33 can be usedindependently of the other. First and second means 32 and 33 can be usedsimultaneously.

[0044] Operation of the device according to the invention was simulatedwith the FLUENT fluid mechanics code. FIG. 6 shows the end of theseparator. The numerical simulation results can be seen in FIG. 6: thedistribution of the oil and of the water forming a petroleum effluentthat circulates in the device according to the invention.

[0045] It can be observed in FIG. 6 that, on the one hand, the water 40is distributed above surface 18 (i.e. in the lower part of channel 19)and, on the other hand, the oil 41 is distributed below surface 18 (i.e.in the upper part of channel 19).

[0046] Implementation of surface 32 or of mask 33 according to theinvention allows to increase the value of the separated water fractionby about 25% in relation to the device provided with opening 22 withoutsurface 32 and without mask 33.

1. A device for separating an effluent comprising phases of differentdensity and conductivity, said device comprising a pair of electrodes(12, 13), means (10) for introducing the effluent between saidelectrodes, a helical channel (19) in which said effluent iscentrifuged, after passage between said electrodes, so that the phasesare separated, and means (4) intended for discharge of the separatedphases, discharge means (4) comprising an opening (22) extending overthe periphery of said centrifuged effluent to discharge part of thecentrifuged effluent, characterized in that the discharge means furthercomprise sealing means (32; 33) for limiting discharge of the less densephase through said opening (22).
 2. A device as claimed in claim 1,wherein the sealing means comprise a mask (33) closing said opening (22)and leaving an orifice (34) so that the denser phase distributed in thelower part of said channel (19) is discharged through said orifice (34)and the less dense phase distributed in the upper part of said channel(19) is kept inside discharge means (4) by said mask (33).
 3. A deviceas claimed in claim 1, wherein the sealing means comprise a surface (32)converging towards the inside of discharge means (4), so that part ofthe effluent discharged through said opening (22) is collected by saidsurface and fed into discharge means (4).
 4. A device as claimed inclaim 3, wherein said surface (32) is truncated-cone-shaped.
 5. A deviceas claimed in claim 2, wherein said orifice (34) extends over an angularportion ranging between 20° and 180°.
 6. A device as claimed in claim 1,wherein said helical channel consists of at least one helical wall (18)arranged in an annular space.
 7. A device as claimed in claim 6, whereinthe end of said wall (18) coincides with an edge of said orifice (34).8. A device as claimed in claim 6, wherein said orifice (34) extends oneither side of the end of said wall (18).
 9. A device as claimed inclaim 6, wherein said helical wall is in contact with internal tube (17)but provides a clearance (d) with the wall of external tube (16).
 10. Adevice as claimed in 1, wherein said helical channel consists of ahelical tube.
 11. A device as claimed in claim 1, wherein saidelectrodes have the shape of cylinders (12, 13) arranged along the sameaxis.
 12. A device as claimed in claim 1, wherein the section of flow ofsaid helical channel is so determined that the velocity of the effluentincreases in relation to the velocity of the effluent in the vicinity ofsaid electrodes.
 13. A device as claimed in claim 1, wherein the lessdense phase is discharged through an axial line.
 14. A device as claimedin claim 1, wherein the discharge means comprise a cyclone (20) and anaxial orifice (21) for discharge of at least part of the centrifugedphase.